A diverse class of data storage systems use rotatable discs as recording media. Although these systems are usually categorized by the type of media (fixed/removable, optical/magnetic, etc.), some things are common to all. Basically, these systems use a lens, a magneto-resistive (MR) element, or another suitable head positioned adjacent a disc to read portions of concentric tracks on a disc, and associated electronics that control the generation of signals carrying digital data to be stored. Subsequently, the transitions stored on the disc surface are sensed so that the stored data can be retrieved.
As discussed in U.S. Pat. No. 4,799,112 (“Method and Apparatus for Recording Data”) issued Jan. 17, 1989 to Bremmer et al., the performance of such a system can be improved by grouping each disc's tracks into annular zones, each of which has certain properties that are kept uniform. The annular zones are separated by zone boundaries, across which the controlled properties may change abruptly. Conventionally, these have included such properties as circumferential bit density or data frequency. The Bremmer et al. patent discloses a circuit for implementing this approach to data storage optimization and further discloses a method for selecting the zone frequencies and track-to-zone assignments in a way that will result in a substantially constant error rate in the writing and subsequent reading of data on and from all tracks on the disc.
More recently, many disc drive applications have adopted configurations using storage discs with annular zones. Moreover, an increasing number of reading and writing subsystems in a disc drive have begun to operate differently, in a zone-dependent fashion. In particular, many modern disc drives use the drive's primary processor to update the head's operating parameters and/or read channel registers via a serial bus, bit by bit. Performing such updates in this manner burdens the primary processor significantly and sporadically, especially when the number of values to be updated exceeds ten and when the zone to be read from switches frequently. Unfortunately, this interferes significantly with the processor's ability to perform its other functions.